Not applicable.
Not Applicable.
This invention relates to preparing copper surfaces for bonding to substrates used in the manufacture of printed circuit boards (PCB""s). More particularly, the invention relates to the manufacture of multilayer PCB""s.
Multilayer PCB""s are constructed by interleaving imaged conductive layers of copper with dielectric layers to make a multilayer sandwich. The dielectric layers are organic resin layers that bond the copper layers together. Typically, the layers of copper and dielectric are bonded together by the application of heat and pressure. The surface of the copper is smooth, however, and does not bond easily to the dielectric layer.
Improved bonding can be achieved by etching or otherwise roughening the surface of the copper to provide microscopic crevices and ridges in the surface of the copper. For example, mechanical means may be used to roughen the copper surface. Unfortunately, delicate circuit patterns are susceptible to damage if mechanically roughened. Thus, there is a need for a copper surface roughening process that does not require mechanical roughening of the copper surface.
Oxide processes are also known in which an oxide having a rough surface is formed on the copper surface. The oxide may be formed by chemical treatment of the copper. One such oxide process is described in U.S. Pat. No. 4,512,818, which provides a treatment solution for the formation of black oxide layers on copper surfaces of multi-layered printed circuits. The treatment solution comprises an oxidant and a hydroxide and is characterized by the addition of a water soluble or dispersible polymer to regulate the properties of the black oxide solution.
Another oxide process is described in U.S. Pat. No. 5,861,076. The ""076 patent describes a bond enhancement process for promoting strong, stable adhesive bonds between surfaces of copper foil and adjacent resin impregnated substrates or superimposed metallic sublayers. According to the process of the invention, a black oxide-coated copper surface is treated with an aqueous reducing solution containing sodium metabisulfite and sodium sulfide to convert the black oxide coating to a roughened metallic copper coating. The roughened metallic copper-coated surface is then passivated and laminated to a resin impregnated substrate.
U.S. Pat. No. 5,492,595 also pertains to an oxide roughening process. The ""595 patent describes a method for treating an oxidized surface of a copper film for bonding to a resinous layer. According to the method of the invention, an oxidized surface of a copper film having cupric oxide whiskers protruding therefrom is contacted with an acidic reducing solution containing thiosulfate to produce a reduced copper surface. The reduced copper surface is then rinsed with an acidic solution, and preferably treated with a passivating agent to minimize any reoxidation prior to laminate formation. A preferred passivating agent is 2-mercaptobenzothiazole.
Oxide processes, while well known, have many shortcomings. A typical oxide process is run at such high temperatures that the substrate is often distorted, leading to quality control problems and additional production costs. The oxidation process is also associated with uniformity problems in which portions of the copper surface are not oxidized or coated by the oxidizing solution. Uniformity problems lead to partial delamination in the multilayer PCB""s. To avoid this problem the PCB is often run through multiple passes to obtain a more uniform oxide coating. Performing multiple passes adds considerably to production cost. Thus, there is a need for a copper roughening process that does not require multiple passes or high temperature, and that does not suffer from the uniformity problems of conventional oxide processes.
Another shortcoming of the typical chemical oxide modification process is that a strong reducing agent, such as dimethylamine borane, is applied to the oxide coating to obtain an even oxide coating. This type of adhesion promotion process produces an oxide coating that is fragile and prone to scratching during handling. Inspection of the circuitry prior to lamination is difficult because of the fragility of the oxide coating. Therefore, there is a need for an adhesion promotion process that permits a less problematic inspection after the adhesion promotion process and prior to the lamination step.
In response to the various problems associated with traditional oxide processes, and in particular their time consuming nature and high processing temperatures, alternative oxide coating processes have been developed. These alternative processes combine the oxidation function of the traditional processes with a controlled etch that actually roughens the underlying copper surface while oxidizing it at the same time. These alternative oxide coating processes tend to be much faster than traditional oxide processes because they form bonds with increased strength and therefore do not require multiple passes. In addition, the alternative methods do not require high temperature processing.
One alternative oxide coating process is described in U.S. Pat. No. 5,800,859. The process includes a treating step in which a metal surface is contacted with an adhesion promotion material. The adhesion promotion material includes 0.1 to 20% by weight hydrogen peroxide, an inorganic acid, an organic corrosion inhibitor and a surfactant. The surfactant is preferably a cationic surfactant, usually an amine surfactant and most preferably a quaternary ammonium surfactant.
Another alternative oxide coating process is described in U.S. patent application Ser. No. 09/479,089, which is incorporated herein by reference in its entirety. The ""089 application describes a method and composition for providing roughened copper surfaces suitable for subsequent multilayer lamination. The method involves contacting a smooth copper surface with an adhesion promoting composition which includes an oxidizer, a pH adjuster, a topography modifier, and either a coating promoter or a uniformity enhancer.
While alternative oxide processes such as that described the ""089 application are advantageous over conventional oxide coating processes for a variety of reasons, the roughened copper surfaces formed by such processes exhibit chemical sensitivity and thus tend to be susceptible to chemical attack. Chemical attack typically occurs during post lamination processing steps. After a multilayer copper and dielectric sandwich is formed through the lamination process, certain post lamination processing steps are performed to prepare the multilayer PCB.
For example, xe2x80x9cthrough-holesxe2x80x9d are drilled through the multilayer sandwich in order to connect the inner layers of the circuit board. The act of drilling these holes typically leaves traces of resin smear on the through-hole interconnections that must be removed by a desmear process. One desmear process involves the application of a solvent sweller and a permanganate etch which can chemically attack the bond between the copper surface and dielectric resin at the site of the through holes. The permanganate etch is typically followed by an acid neutralizer which can also chemically attack the bond and cause delamination. While other through-hole cleaning techniques are known, such as plasma etch or laser ablation, these processes generate intense heat which can also attack the copper/resin interface.
Once the desmear process is completed, the drilled holes are made conductive through direct metalization or similar processes. These processes involve numerous alkaline and acid processing steps, all of which can chemically attack the copper/resin interface. Further, the conductive through-hole is usually sealed with a layer of electrolytic copper. The electrolytic process involves alkaline and acidic baths which can also lead to chemical attack of the through-hole interconnects. The result of these chemical attacks is the delamination of the sandwich layers in the area of the through holes.
The chemically attacked area is termed xe2x80x9cpink ringxe2x80x9d or xe2x80x9cwedge voidxe2x80x9d in the circuit board industry. The formation of pink rings or wedge voids represents serious defects in the PCB""S, especially in an era when increasingly high quality and reliability are demanded in the PCB industry. Thus, there is a need for an improved alternative oxide coating process that provides a surface that is less susceptible to chemical attack during post-lamination processing steps.
Accordingly, an object of this invention is to provide a copper surface roughening process that does not require mechanical roughening of the copper surface.
Another object is to provide a copper surface roughening process that does not suffer from the uniformity problems of conventional oxide processes.
A further object is to provide a copper surface roughening process that does not require multiple passes or high temperature.
Yet another object is to provide a copper surface roughening process that provides a surface that is less susceptible to chemical attack during post-lamination processing steps.
A further object is to provide an improved alternative oxide coating process and composition that provides a surface that is less susceptible to chemical attack during post-lamination processing steps than at least some other alternative oxide coating processes and compositions.
A yet further object is to provide a copper surface roughening process that provides a surface that is more acid resistant during post-lamination processing steps.
Another object is to provide an improved alternative oxide coating process and composition that provides a surface that is more acid resistant during post-lamination processing steps than at least some other alternative oxide coating processes and compositions.
At least one of these objects is addressed, in whole or in part, by the present invention. In one embodiment, the invention is a composition and method for roughening a copper surface in order to provide higher bond strengths between the copper and dielectric resin layers in a multilayer PCB, where such bonds are also resistant to chemical attack. The composition comprises an oxidizer, a pH adjuster, a topography modifier, and a coating stabilizer. In another embodiment, the invention is a process for preparing roughened copper surfaces suitable for subsequent multilayer lamination. The process involves contacting a copper surface with an adhesion promoting composition under conditions effective to provide a roughened copper surface, and then contacting the roughened copper surface with an acid resistance promoting composition.
While the invention will be described in connection with several embodiments, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention includes all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.
As noted above, one aspect of the present invention is an adhesion promoting composition which provides a roughened copper surface, comprising an oxidizer, a pH adjuster, a topography modifier, and a coating stabilizer.
Any suitable oxidizer known in the art may be used in the inventive composition. Suitable oxidizers include hydrogen peroxide. The oxidizer may be present in the range between about 0.05 wt % and about 5 wt %, alternatively in the range between about 0.1 wt % and about 4 wt %. As yet another alternative, the oxidizer may be present in the range between about 0.5 wt % and about 3 wt %, alternatively in the range between about 0.5 wt % and about 2 wt %. Proportions of oxidizer in this specification are based on undiluted quantities, although it will be recognized that, in practice, the oxidizers are typically part of an aqueous solution when added to the composition.
If hydrogen peroxide is used as the oxidizer, a hydrogen peroxide stabilizer may be used (although the use of a stabilizer is not required to practice this invention). Non-limiting examples of optional hydrogen peroxide stabilizers include: alkyl monoamines having 2 to 10 carbon atoms, and their salts; polymethylenediamines having 4 to 12 carbon atoms and their salts; alkoxyamines formed by substituting at least one hydrogen atom of ammonia by an alkoxy radical having 2 to 6 carbon atoms and alkoxyamines formed by substituting at least one hydrogen atom connected with the nitrogen atom of an alkyl monoamine having 2 to 10 carbon atoms by an alkoxy radical having 2 to 6 carbon atoms; alkyl acyl radical formed by substituting at least one hydrogen atom of ammonia by an alkyl acyl radical having 3 to 6 carbon atoms, and at least one alkyl acid amide formed by substituting at least one alkyl monoamine having 2 to 10 carbon atoms by an alkyl acyl radical having 3 to 6 carbon atoms; alicyclic imines having a 5 to 8 membered ring; mono-n-propylamine, di-n-propylamine, tri-n-propylamine and hexamethylenediamine; octylamine; and propionylamide. In addition, U.S. Pat. Nos. 3,756,957, and 5,800,859 describe a range of suitable hydrogen peroxide stabilizers; U.S. Pat. Nos. 3,756,957 and 5,800,859 are hereby incorporated by reference in their entirety. An example of a suitable hydrogen peroxide stabilizer from the categories in these patents is sodium phenolsulfonate.
If a hydrogen peroxide stabilizer is used, it may be present in the composition in an amount of from about 0.001 wt % to about 5 wt %, alternatively in an amount of from about 0.005 wt % to about 1 wt %. Alternatively, the hydrogen peroxide stabilizer may be present in the composition in an amount effective to achieve the purpose of stabilizing the hydrogen peroxide to the desired degree.
The choice of pH adjuster is not critical. Any suitable organic or inorganic acid may be used, although nitric acid is not preferred. Non-limiting examples of suitable acids include sulfuric, phosphoric, acetic, formic, sulfamic, hydroxy-acetic acid, and mixtures thereof. Alternatively, sulfuric acid may be selected as the pH adjuster. The pH adjuster may be present in the composition in the range between about 0.01% and about 20% by weight and alternatively in the range between about 0.5% and about 10% by weight.
Suitable topography modifiers are five membered aromatic fused N-heterocyclic ring compounds (hereinafter xe2x80x9cN-heterocyclic compoundsxe2x80x9d) with at least one nitrogen atom in the N-heterocyclic ring: 
In the above formula, X may be N or C, and Y may be N or C. The R substituents on the aromatic ring may be H, halogen, hydroxy, alkyl, hydroxyalkyl, amino, aminoalkyl, nitro, nitroalkyl, mercapto, mercaptoalkyl, or alkoxy groups containing from 1 to about 10 or more carbon atoms. Specific examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, amyl, etc. At least one of the nitrogen atoms in the heterocyclic ring depicted above is bonded directly to a hydrogen atom. The nitrogen atom at the #1 position in the heterocyclic ring is preferably, but not necessarily, bonded to a hydrogen atom. Non-limiting examples of suitable topography modifiers include 1H-benzotriazole (CAS registration number, xe2x80x9cCASxe2x80x9d: 95-14-7), 1H-indole (CAS 120-72-9), 1H-indazole (CAS 271-44-3), and 1H-benzimidazole (CAS 51-17-2). Derivatives of N-heterocyclic compounds suitable as topography modifiers include N-heterocyclic compounds with a hydrogen atom bonded to the nitrogen atom at the #1 position in the heterocyclic ring.
Non-limiting examples of suitable derivatives of 1H-benzotriazole (CAS 95-14-7) suitable for use as topography modifiers include: 5-methyl-1H-benzotriazole (CAS 136-85-6), 6-Nitro-1H-benzotriazole (CAS 2338-12-7), 1H-naphtho(1,2-d)triazole (CAS 233-59-0), and 1H-Naphtho[2,3-d]triazole (CAS 269-12-5).
Non-limiting examples of suitable derivatives of indole (1H-Indole; CAS 120-72-9) suitable for use as topography modifiers include: 5-Aminoindole (1H-Indol-5-amine; CAS 5192-03-0), 6-methylindole (1H-Indole, 6-methyl-; CAS 3420-O2-8), 1H-indole-5-methyl (CAS 614-96-0), 7-methylindol (1H-Indole, 7-methyl-; CAS 933-67-5), 3-methylindole (1H-Indole, 3-methyl-; CAS 83-34-1), 2-Methylindole (2-Methyl-1H-indole; CAS 95-20-5), 1H-Indole, 3,5-dimethyl-(CAS 3189-12-6), 2,3-Dimethylindole (1H-Indole, 2,3-dimethyl-; CAS 91-55-4), and 2,6-dimethylindole (1H-Indole, 2,6-dimethyl-; CAS 5649-36-5).
Non-limiting examples of suitable derivatives of 1H-indazole (CAS 271-44-3) suitable for use as topography modifiers include: 1H-Indazol-5-amine (CAS 19335-11-6) and 3-Chloro-1H-indazole (CAS 29110-74-5).
Non-limiting examples of suitable derivatives of 1H-benzimidazole (CAS 51-17-2) suitable for use as topography modifiers include: 2-Hydroxy-1H-benzimidazole (CAS 615-16-7), 2-Methyl-1H-benzimidazole (CAS 615-15-6), and 2-(methylthio)-1H-Benzimidazole (CAS 7152-24-1).
The topography modifier may be present in the range between about 0.1 g/l (grams per liter) and about 20 g/l, alternatively in the range between about 0.5 g/l and about 7 g/l. For example, 1H-benzotriazole can be present in the range between about 0.1 g/l and about 20 g/l, alternatively in the range between about 0.5 g/l and about 7 g/l.
The topography modifier is thought to vary the surface characteristics of the copper during treatment of the copper surface with the adhesion promoting solution of the invention. During treatment with the adhesion promoting composition of the invention, the copper surface is believed to comprise a complex of copper together with the topography modifier to produce a greater surface area than would be possible without the topography modifier. As a result, the topography modifier has a beneficial effect on peel strengthxe2x80x94indeed, peel strength is dramatically reduced if the topography modifier is not used in the adhesion promoting solution. The inventors do not intend the foregoing theory to limit the invention to processes or products that operate as specified by this theory. Any inaccuracy in this theory does not limit the scope of the present invention.
The coating stabilizer is a sulfur compound that renders the roughened copper surface more chemically resistant to subsequent chemical processing. A suitable coating stabilizer may have the following formula: 
wherein X1 is S or Nxe2x80x94R9, and wherein X2 is S or Nxe2x80x94R10. The R groups are independently selected from H, halogen, S, epoxide, glycol, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, a C1 up to C18 alkyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a cycloalkyl which may be singly or multiply substituted in singular or multiply bonded fashion, a heterocyclic which may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkenyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkadienyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkynyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, an aryl which may be singly or multiply substituted in singular or multiply bonded fashion, a heteroaryl which may be singly or multiply substituted in singular or multiply bonded fashion, an alkylaryl which may be singly or multiply substituted in singular or multiply bonded fashion, an arylalkyl which may be singly or multiply substituted in singular or multiply bonded fashion, and combinations thereof, wherein the substituents are selected from the group consisting of halogen, epoxide, glycol, N, O, S, haloalkyl, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, alkyl, aryl, and combinations thereof. In addition, any two or more of R1-10 may form a linkage or linkages comprising any of the groups identified above suitable for forming such linkages. Depending on the linkage, some of R1-10 may drop out. For example, if R2 and R3 form an aromatic linkage such as a benzene ring, then R1 and R4 will be nothing. The same holds true for the remainder of R1-8: one substituent of each pair R1 and R2, R3 and R4, R5 and R6, and R7 and R8 will be nothing if the other substituent in the pair is part of an aromatic linkage.
Suitable coating stabilizers falling within formula (I) include the following: 2-mercapto benzothiazole; 2,2xe2x80x2-dithiobis(benzothiazole); 6-ethoxy-2-mercaptobenzothiazole; 2-mercaptothiazoline; and 3,4,5,6-tetrahydro-2-pyrimidinethiol. Alternatively, 2-mercaptothiazoline may be used as the coating stabilizer.
The coating stabilizer may, in the alternative, have the following formula: 
wherein Z2 is Li, Na, K or NH4, wherein X1 is S or Nxe2x80x94R6, and wherein X2 is S or Nxe2x80x94R7. The R groups are independently selected from H, halogen, S, epoxide, glycol, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, a C1 up to C18 alkyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a cycloalkyl which may be singly or multiply substituted in singular or multiply bonded fashion, a heterocyclic which may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkenyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkadienyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkynyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, an aryl which may be singly or multiply substituted in singular or multiply bonded fashion, a heteroaryl which may be singly or multiply substituted in singular or multiply bonded fashion, an alkylaryl which may be singly or multiply substituted in singular or multiply bonded fashion, an arylalkyl which may be singly or multiply substituted in singular or multiply bonded fashion, and combinations thereof, wherein the substituents are selected from halogen, epoxide, glycol, N, O, S, haloalkyl, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, alkyl, aryl, and combinations thereof. In addition, any two or more of R1-7 may form a linkage or linkages comprising any of the groups identified above suitable for forming such linkages.
Suitable coating stabilizers falling within formula (II) include the following: 2-imidazolidinethione; potassium 3-(thiocarbamoyl)-dithiocarbazate; sodium diethyldithiocarbamate; sodium dimethyldithiocarbamate; tetraethylthiuram disulfide; tetramethylthiuram disulfide; and 2,5-dithiobiurea. Alternatively, sodium diethyldithiocarbamate may be used as the coating stabilizer.
The coating stabilizer may be present in the composition in the range between about 1 to about 1000 ppm, alternatively in the range between about 2 to about 200 ppm, alternatively in the range between about 50 to about 150 ppm, alternatively about 100 ppm. For example, 2-mercaptothiazoline can be present at about 100 ppm.
The inventive composition for roughening a copper surface may also optionally include a uniformity enhancer and/or a coating promoter. The optional uniformity enhancer may be a tetrazole such as 1H-tetrazole (CAS 288-94-8) and its derivatives: 
The R1 and R2 substituents on the tetrazole ring may be hydroxyl, amino, alkyl, hydroxyalkyl, aminoalkyl, nitroalkyl, mercaptoalkyl, or alkoxy groups containing from 1 to about 10 or more carbon atoms. Specific examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, amyl, etc. Non-limiting examples of suitable tetrazole derivatives that can be used in the present invention as a uniformity enhancer include: 5-aminotetrazole (CAS 5378-49-4), 5-methyltetrazole (CAS 4076-36-2), 5-methylaminotetrazole (CAS 53010-03-0), 1H-tetrazol-5-amine (CAS 4418-61-5), 1H-tetrazol-5-amine, N,N-dimethyl-(CAS 5422-45-7), 1-methyltetrazole (CAS 16681-77-9), 1-methyl-5-mercaptotetrazole, 1,5-dimethyltetrazole (CAS 5144-11-6), 1-methyl-5-aminotetrazole (CAS 5422-44-6), and 1-methyl-5-methylamino-tetrazole (CAS 17267-51-5).
The optional uniformity enhancer may be present in an amount effective to enhance the uniformity of the roughened copper surface. Alternatively, the uniformity enhancer may be present in the range between about 0.01 to about 10 g/l, alternatively in the range between about 0.1 to about 5 g/l, alternatively in the range between about 0.3 to about 1 g/l, alternatively at about 0.5 g/l. For example, 5-aminotetrazole can be present at about 0.5 g/l.
The optional coating promoter is a five membered aromatic fused N-heterocyclic ring compound with 1 to 3 nitrogen atoms in the fused ring, wherein none of the 1 to 3 nitrogen atoms in the fused ring are bonded to a hydrogen atom: 
In the above formula, X may be N or C, and Y may be N or C. The R substituents on the aromatic ring may be H, halogen, hydroxy, alkyl, hydroxyalkyl, amino, aminoalkyl, nitro, nitroalkyl, mercapto, mercaptoalkyl, or alkoxy groups containing from 1 to about 10 or more carbon atoms. The R1 substituents on the heterocyclic ring bonded to the nitrogen atom at the #1 position may be hydroxyl, amino, alkyl, hydroxyalkyl, aminoalkyl, nitroalkyl, mercaptoalkyl, or alkoxy groups. Specific examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, amyl, etc. Non-limiting examples of optional coating promoters suitable for use in the present invention include: 1-hydroxybenzotriazole (CAS 2592-95-2), 1-methylindole (CAS 603-76-9), 1-methylbenzotriazole (CAS 13351-73-0), 1-methylbenzimidazole (CAS 1632-83-3), 1-methylindazole (CAS 13436-48-1), 1-ethyl-indazole (CAS 43120-22-5), 1H-Indole, 1,5-dimethyl-indole (CAS 27816-53-1), 1,3-dimethyl-indole (CAS 875-30-9), methyl 1-(butylcarbamoyl)-2-benzimidazolecarbonate, 1-(chloromethyl)-1H-benzotriazole, and 1-aminobenzotriazole.
The optional coating promoting may be present in an amount effective to enhance the coating characteristics of the composition. Alternatively, the coating promoter may be present in the range between about 0.01 to about 10 g/l, alternatively in the range between about 0.1 to about 5 g/l, alternatively in the range between about 0.3 to about 3 g/l, alternatively at about 2 g/l. For example, 1-hydroxybenzotriazole can be present at about 2 g/l.
The formulation of the inventive composition for roughening a copper surface may be made up with de-ionized water.
The inventive composition for roughening a copper surface does not require halogen ions and can be free of halogen ions, if desired. The inventors define xe2x80x9chalogen ionsxe2x80x9d as fluoride, chloride, bromide or iodide ions or any combination or equivalent of these ions in aqueous solution. In addition, the composition of the present invention does not require a surfactant to achieve an excellent roughened copper surface.
Halogens can, however, be employed in the formulation if desired. For example, a small amount of chloride ion or other halide ions can be used in the formulation. If employed, halide ions may be present in the range between about 0.1 ppm to about 1000 ppm, alternatively in the range between about 1 ppm to about 100 ppm.
The adhesion promoting composition may optionally comprise a copper salt such as copper sulfate. The aqueous copper ions protect virgin stainless steel surfaces, such as those of a process tank, from chemical attack. Hence it is advantageous to include a quantity of copper salt in the adhesion promoting composition if the copper surface to be treated is dipped into a new or previously unused steel tank. However, there is no requirement to include a copper salt to obtain a highly satisfactory roughened copper surface.
The adhesion promoting composition may also optionally contain a water soluble polymer. Any water soluble polymer known in the art may be used in the present adhesion promoting composition. Suitable water soluble polymers include polymers of ethylene oxide and propylene oxide, polyethylene glycols, polypropylene glycols, and polyvinyl alcohols. The water soluble polymer may be present in the range of between about 0.01 wt % and about 5 wt %, alternatively in the range of between about 0.05 wt % and about 3 wt %, alternatively in the range of between about 0.1 wt % and about 1 wt %, alternatively at about 0.5 wt %. Polyethylene glycol may be selected as the optional water soluble polymer. One suitable source of polyethylene glycol is the product Pluracol(copyright) E2000 sold by the BASF Corporation.
A copper surface can be treated with the adhesion promoting composition in a variety of ways, including (but not limited to) immersion in a bath, dipping in a bath, or spraying. The treatment may take place at any temperature and for any duration suitable to obtain the desired uniformed roughened copper surface. For example, suitable roughened copper surfaces may be obtained where the temperature during treatment is in the range from about 40xc2x0 F. to about 180xc2x0 F. (about 4xc2x0 C. to about 82xc2x0 C.), alternatively from about 70xc2x0 F. to about 150xc2x0 F. (about 21xc2x0 C. to about 66xc2x0 C.), alternatively from about 80xc2x0 F. to about 120xc2x0 F. (about 27xc2x0 C. to about 49xc2x0 C.), alternatively about 100xc2x0 F. (about 38xc2x0 C.). Suitable roughened copper surfaces may also be obtained with temperatures outside of these ranges, however. With respect to duration, the adhesion promoting composition may, for example, be contacted with the copper surface for about 1 second to about 1 hour, alternatively from about 10 seconds to about 10 minutes, alternatively from about 30 seconds to about 5 minutes, alternatively for about 1 minute. Suitable roughened copper surfaces may also be obtained with contact durations outside of these ranges, however.
In keeping with another aspect of the present invention, the process of preparing roughened copper surfaces suitable for subsequent multilayer lamination includes the following steps, some of which are optional:
(i) Providing a substantially clean copper surface, optionally by applying a highly built alkaline cleaning solution to a copper surface. The highly built alkaline cleaning solution comprises a surfactant and a phosphate or a phosphate ester.
(ii) Optionally dipping the substantially clean copper surface into a pre-dip to condition the surface and/or to remove surplus cleaning solution from the copper surface providing a clean copper surface. One suitable optional pre-dip may comprise an oxidizer, a pH adjuster and a topography modifier, as those components are described above. The oxidizer and topography modifier may be in the pre-dip in the ranges described above. The pH adjuster may be in the pre-dip in the range between about 0.005% and about 10% by weight and alternatively in the range between about 0.01% and about 5% by weight. A hydrogen peroxide stabilizer may be used if hydrogen peroxide is used as the oxidizer. The hydrogen peroxide stabilizer may be selected from the various stabilizers described above and may be in the pre-dip in the ranges described above. Other suitable pre-dips that will be known to those of skill in the art may also be used. The pre-dip treatment may take place at any temperature and for any duration suitable to obtain the desired conditioning and/or cleaning, including the temperatures and durations discussed above for application of the adhesion promoting composition.
(iii) Applying to the clean copper surface an adhesion promoting composition comprising an oxidizer, a pH adjuster, a topography modifier, a coating stabilizer, and optionally, other optional components as described above.
(iv) Optionally dipping the uniformly roughened copper surface into a post-dip to provide a roughened copper surface suitable for subsequent multilayer lamination. The optional post-dip is used to coat the roughened copper surface with a coating of organic molecules to enable enhanced bonding between the roughened copper surface and a suitable dielectric resin. The post-dip solution comprises an azole or silane compound. The post-dip may further comprise a titanate, zirconate, or aluminate.
Step (i) may further include draining excess cleaning solution from the copper surface.
Non-limiting examples of silanes for enhancing the bond strength between the copper surface and the dielectric include any trichloro or trimethoxy silane, especially those derivatives with at least one nitrogen atom such as trimethoxysilylpropyldiethylenetriamine. Other examples of silanes suitable for use in the present invention include:
3-methylacryloyloxypropyltrimethoxysilane,
3-(N-styrylmethyl-2aminoethylamino) propyltrimethoxysilane hydrochloride,
3-(N-allyl-2-aminoethylamino)-propyltrimethoxysilane hydrochloride,
N-(styrylmethyl)-3-aminopropyltrimethoxysilane hydrochloride,
N-2-aminoethyl-3-aminopropyltrimethoxysilane,
3-(N-Benzyl-2-aminoethylamino)-propyltrimethoxy silane hydrochloride,
beta-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, gamma-aminopropyl-triethoxy silane,
gamma-glycidoxypropyltrimethoxysilane, and vinyltrimethoxysilane.
Non-limiting examples of titanates that can be used in the present invention include:
titanate amine,
tetraocytl di(ditridecyl)phosphito titanate,
tetra(2,2-diallyloxymethyl) butyl-di(ditridecyl)phosphito titanate,
neopentyl(diallyl)oxytri(diocytl)pryo-phosphato titante, and
neopentyl(diallyl)oxy tri(m-amino)phenyl titanate.
Non-limiting examples of suitable zirconates (available, for example, from Kenrich Petrochemicals, Inc., Bayonne, N.J.) include:
KZ 55-tetra (2,2 diallyloxymethyl)butyl,
di(ditridecyl)phosphito zirconate,
NZ-01-neopentyl(diallyl)oxy,
trineodecanoyl zirconate, and
NZ-09-neopentyl(diallyl)oxy, tri(dodecyl)benzene-sulfonyl zirconate.
Further non-limiting examples of suitable zirconates include: tetra (2,2 diallyloxymethyl)butyl-di(ditridecyl)phosphito zirconate, and zirconium IV 2,2-dimethyl 1,3-propanediol.
Non-limiting examples of aluminates that can be used in the present invention include: Kenrich(copyright) diisobutyl(oleyl)acetoacetylaluminate (KA 301), and diisopropyl(oleyl)acetoacetyl aluminate (KA 322).
The inventors have found that the use of a coating stabilizer in the inventive adhesion promoting composition, as described above, renders the coating on the copper surface more chemically resistant to subsequent processing than alternative oxide coating processes known in the art which do not use such stabilizer. Another aspect of the present invention is a process in which a copper surface is treated with an adhesion promoting composition in which a coating stabilizer is optional, and then subsequently contacted with a composition that promotes acid resistance. In other words, the roughened copper surface is made resistant to chemical attack by a separate application of an acid resistance promoting composition after the adhesion promoting composition has been applied.
The inventors discovered that this two-step approach is particularly advantageous from a manufacturing standpoint. In particular, it was discovered that some of the coating stabilizers described above are themselves susceptible to chemical attack. When such coating stabilizers are added directly to an adhesion promoting bath which contains a pH adjuster, such as sulfuric acid, they tend to decompose over time into their synthetic components. After such decomposition, the baths no longer produce an acid resistant coating on the copper surface. Typically, decomposition of the coating stabilizer occurs within 30 minutes to 4 hours of addition. The cost associated with continually refreshing the baths to avoid the effects of this decomposition render this process less desirable for commercial manufacturing purposes.
The inventive process which avoids these decomposition issues comprises the steps of (1) contacting with a clean copper surface an adhesion promoting composition under conditions effective to provide a roughened copper surface, and (2) contacting the roughened copper surface with an acid resistance promoting composition.
The adhesion promoting composition is the same as that described above, with the exception that the coating stabilizer is an optional component, and is preferably absent. Thus, the adhesion promoting composition comprises an oxidizer, a pH adjuster, a topography modifier, and, optionally, a coating stabilizer as well as any of the other optional components described above. The adhesion promoting composition may be applied to the copper surface in any of the various manners and under any of the various conditions described above.
Suitable acid resistance promoting compositions include thio compounds, particularly thiocarbamates, thiocarbonates, xanthates, and sulfides. Alternatively, the acid resistance promoting composition is a sulfur-containing compound which may have the following formula:
xe2x80x83(S)Axe2x80x94X1xe2x80x83xe2x80x83(III)
wherein A is 1-20 (alternatively A may be 1-10 or 1-5) and X1 is Mg, Ca, Li2, Na2, K2, or (NH4)2. As yet another alternative, the acid resistance promoting composition may have the following formula: 
wherein A is 1-20 (alternatively A may be 1-10 or 1-5) and X1 is Mg, Ca, Li2, Na2, K2, or (NH4)2.
As yet another alternative, the acid resistance promoting composition may have the following formula: 
wherein 
Oxe2x80x94R3, or Sxe2x80x94R3, wherein A is 1-20, wherein X2 is Li, 
wherein W2 is 
Oxe2x80x94R6, or Sxe2x80x94R6, and wherein B is 1-20. A may also be 1-10 or 1-5.
The R groups are independently selected from H, halogen, S, epoxide, glycol, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, a C1 up to C18 alkyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a cycloalkyl which may be singly or multiply substituted in singular or multiply bonded fashion, a heterocyclic which may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkenyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkadienyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, a C1 up to C18 alkynyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, an aryl which may be singly or multiply substituted in singular or multiply bonded fashion, a heteroaryl which may be singly or multiply substituted in singular or multiply bonded fashion, an alkylaryl which may be singly or multiply substituted in singular or multiply bonded fashion, an arylalkyl which may be singly or multiply substituted in singular or multiply bonded fashion, and combinations thereof, wherein the substituents are selected from the group consisting of halogen, epoxide, glycol, N, O, S, haloalkyl, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, alkyl, aryl, and combinations thereof. In addition, any two adjacent of R1-6 may form a linkage or linkages comprising any of the groups identified above suitable for forming such linkages.
Suitable acid resistance promoting compositions falling with formulas (III), (IV) and (V) above include: sodium dialkyl dithio carbamates, sodium dialkyl polythiocarbamates, sodium dialkyl trithio carbonates, sodium dialkyl polythiocarbonates, sodium diaryl dithio carbamates, sodium diaryl polythiocarbamates, sodium diaryl trithio carbonates, sodium diaryl polythiocarbonates, sodium alkylaryl dithio carbamates, sodium alkylaryl polythiocarbamates, sodium alkylaryl trithio carbonates, sodium alkylaryl polythiocarbonates, potassium dialkyl dithio carbamates, potassium dialkyl polythiocarbamates, potassium dialkyl trithio carbonates, potassium dialkyl polythiocarbonates, potassium diaryl dithio carbamates, potassium diaryl polythiocarbamates, potassium diaryl trithio carbonates, potassium diaryl polythiocarbonates, potassium alkylaryl dithio carbamates, potassium alkylaryl polythiocarbamates, potassium alkylaryl trithio carbonates, potassium alkylaryl polythiocarbonates, ammonium dialkyl dithio carbamates, ammonium dialkyl polythiocarbamates, ammonium dialkyl trithio carbonates, ammonium dialkyl polythiocarbonates, ammonium diaryl dithio carbamates, ammonium diaryl polythiocarbamates, ammonium diaryl trithio carbonates, ammonium diaryl polythiocarbonates, ammonium alkylaryl dithio carbamates, ammonium alkylaryl polythiocarbamates, ammonium alkylaryl trithio carbonates, ammonium alkylaryl polythiocarbonates, dialkyl xanthates, diaryl xanthates, alkylaryl xanthates, sulfide, disulfide, trisulfide, tetrasulfide, polysulfide, and combinations thereof, wherein the alkyl component is a C1 up to C18 alkyl which is linear or branched and may be singly or multiply substituted in singular or multiply bonded fashion, wherein the aryl component is an aryl or a heteroaryl which may be singly or multiply substituted in singular or multiply bonded fashion, and wherein the substituents are selected from the group consisting of halogen, halide, epoxide, glycol, N, O, S, haloalkyl, hydroxy, aryloxy, benzyloxy, alkoxy, haloalkoxy, amino, monoalkylamino, dialkylamino, heteroalkylamino, acyloxy, acyl, ketone, quinone, aldehyde, carbohydrate, organometallic, alkyl, aryl, and combinations thereof. Several nonlimiting examples of suitable acid resistance promoting compositions are sodium dioctyldithiocarbamate, disodium trithiocarbonate, sodium sulfide, sodium N,N-dibutyldithiocarbamate, and sodium hydroquinone monomethyl ether xanthate (xe2x80x9cHQMME-xanthatexe2x80x9d).
The acid resistance promoting composition may be contacted with the roughened copper surface in a variety of ways, including (but not limited to) immersion in a bath, dipping in a bath, or spraying. The acid resistance promoting composition may be contacted with the roughened copper surface as an aqueous solution. When applied in this fashion, the composition may be present in the aqueous solution between about 0.1 g/l and about 5 g/l. Alternatively, the composition may be present in the aqueous solution between about 1 g/l and about 3 g/l. As yet another alternative, the composition may be present in the aqueous solution at about 1 g/l.
The acid resistance promoting composition may be contacted with the roughened copper surface for at least about 1 second. Alternatively, the composition may be contacted with the roughened copper surface for between about 1 second to about 5 minutes. As yet another alternative, the composition may be contacted with the roughened copper surface for between about 5 seconds to about 2 minutes.
The acid resistance promoting composition may be contacted with the roughened copper surface at any temperature suitable to obtain the desired acid-resistant roughened copper surface. For example, suitable roughened copper surfaces may be obtained where the temperature during treatment is in the range from about 20xc2x0 F. to about 180xc2x0 F. (about xe2x88x927xc2x0 C. to about 82xc2x0 C.), alternatively from about 40xc2x0 F. to about 150xc2x0 F. (about 4xc2x0 C. to about 66xc2x0 C.), alternatively from about 60xc2x0 F. to about 120xc2x0 F. (about 16xc2x0 C. to about 49xc2x0 C.), alternatively about 70xc2x0 F. (about 21xc2x0 C.), alternatively about room temperature. Suitable acid-resistant roughened copper surfaces may also be obtained with temperatures outside of these ranges, however.
The process of preparing roughened copper surfaces and subsequently post treating the surfaces with an acid resistance promoting composition may also include other optional steps. For instance, the process may comprise the following steps, some of which are optional:
(i) Providing a substantially clean copper surface, optionally by applying a highly built alkaline cleaning solution to a copper surface. The highly built alkaline cleaning solution comprises a surfactant and a phosphate or a phosphate ester.
(ii) Optionally dipping the substantially clean copper surface into a pre-dip to condition the surface and/or to remove surplus cleaning solution from the copper surface providing a clean copper surface. One suitable optional pre-dip may comprise an oxidizer, a pH adjuster and a topography modifier, as those components are described above. The oxidizer and topography modifier may be in the pre-dip in the ranges described above. The pH adjuster may be in the pre-dip in the range between about 0.005% and about 10% by weight and alternatively in the range between about 0.01% and about 5% by weight. A hydrogen peroxide stabilizer may be used if hydrogen peroxide is used as the oxidizer. The hydrogen peroxide stabilizer may be selected from the various stabilizers described above and may be in the pre-dip in the ranges described above. Other suitable pre-dips that will be known to those of skill in the art may also be used. The pre-dip treatment may take place at any temperature and for any duration suitable to obtain the desired conditioning and/or cleaning, including the temperatures and durations discussed above for application of the adhesion promoting composition.
(iii) Applying to the clean copper surface an adhesion promoting composition comprising an oxidizer, a pH adjuster, a topography modifier, optionally a coating stabilizer, and optionally, other optional components as described above, in order to form a roughened copper surface.
(iv) Optionally rinsing the roughened copper surface with water.
(v) Dipping the roughened copper surface in an aqueous solution containing an acid resistance promoting composition, as described above.
(vi) Optionally dipping the uniformly roughened copper surface into a post-dip to provide a roughened copper surface suitable for subsequent multilayer lamination. The optional post-dip is used to coat the roughened copper surface with a coating of organic molecules to enable enhanced bonding between the roughened copper surface and a suitable dielectric resin. The post-dip solution comprises an azole or silane compound. The post-dip may further comprise a titanate, zirconate, or aluminate.
Step (i) may further include draining excess cleaning solution from the copper surface.
The inventors have found that the use of an adhesion promoting composition on a copper surface, followed by subsequent treatment with an acid resistance promoting composition, renders the coating on the copper surface more chemically resistant to subsequent processing than other alternative oxide coating processes known in the art. At the same time, inefficiencies in the manufacturing process are avoided because the acid resistance promoting composition is applied in a separate step and thus is not subject to untimely decomposition due to the acidic nature of the adhesion promoting composition bath.
One practical test that can be used to indicate the better adhesion of resins to the present copper surface is a xe2x80x9cpeel strengthxe2x80x9d test. Self-adhesive tape is adhered to a treated copper surface which has been laminated to a polymeric substrate. The surface is placed into a nitric acid bath to remove the copper from the non-taped regions of the substrate. The tape is removed and the remaining copper is then mechanically peeled away from the substrate while measuring the force needed to accomplish the peel in pounds per inch. Higher peel strengths are typically indicative of a desirable, tightly-adhering coating.
One practical test that can be used to indicate the better resistance to chemical attack of the present copper surfaces is the simple application of an acid solution to the copper surfaces, followed by observation. Such test is described in further detail below in conjunction with the examples.
The following examples represent specific but nonlimiting embodiments of the present invention: